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Subject[PATCH 7/9] iommu/amd: Don't hold a reference to mm_struct
Date
From: Joerg Roedel <jroedel@suse.de>

With mmu_notifiers we don't need to hold a reference to the
mm_struct during the time the pasid is bound to a device. We
can rely on the .mn_release call back to inform us when the
mm_struct goes away.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Oded Gabbay <Oded.Gabbay@amd.com>
---
drivers/iommu/amd_iommu_v2.c | 40 +++++++++++++++++++++++++++++++++-------
1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/amd_iommu_v2.c b/drivers/iommu/amd_iommu_v2.c
index 69a46f1..2b848c0 100644
--- a/drivers/iommu/amd_iommu_v2.c
+++ b/drivers/iommu/amd_iommu_v2.c
@@ -297,7 +297,6 @@ static void put_pasid_state_wait(struct pasid_state *pasid_state)
schedule();

finish_wait(&pasid_state->wq, &wait);
- mmput(pasid_state->mm);
free_pasid_state(pasid_state);
}

@@ -321,6 +320,13 @@ static void unbind_pasid(struct pasid_state *pasid_state)

/* Make sure no more pending faults are in the queue */
flush_workqueue(iommu_wq);
+
+ /*
+ * No more faults are in the work queue and no new faults will be queued
+ * from here on. We can safely set pasid_state->mm to NULL now as the
+ * mm_struct might go away after we return.
+ */
+ pasid_state->mm = NULL;
}

static void free_pasid_states_level1(struct pasid_state **tbl)
@@ -636,6 +642,7 @@ int amd_iommu_bind_pasid(struct pci_dev *pdev, int pasid,
{
struct pasid_state *pasid_state;
struct device_state *dev_state;
+ struct mm_struct *mm;
u16 devid;
int ret;

@@ -659,12 +666,14 @@ int amd_iommu_bind_pasid(struct pci_dev *pdev, int pasid,
if (pasid_state == NULL)
goto out;

+
atomic_set(&pasid_state->count, 1);
init_waitqueue_head(&pasid_state->wq);
spin_lock_init(&pasid_state->lock);

+ mm = get_task_mm(task);
pasid_state->task = task;
- pasid_state->mm = get_task_mm(task);
+ pasid_state->mm = mm;
pasid_state->device_state = dev_state;
pasid_state->pasid = pasid;
pasid_state->invalid = false;
@@ -673,7 +682,7 @@ int amd_iommu_bind_pasid(struct pci_dev *pdev, int pasid,
if (pasid_state->mm == NULL)
goto out_free;

- mmu_notifier_register(&pasid_state->mn, pasid_state->mm);
+ mmu_notifier_register(&pasid_state->mn, mm);

ret = set_pasid_state(dev_state, pasid_state, pasid);
if (ret)
@@ -684,16 +693,23 @@ int amd_iommu_bind_pasid(struct pci_dev *pdev, int pasid,
if (ret)
goto out_clear_state;

+ /*
+ * Drop the reference to the mm_struct here. We rely on the
+ * mmu_notifier release call-back to inform us when the mm
+ * is going away.
+ */
+ mmput(mm);
+
return 0;

out_clear_state:
clear_pasid_state(dev_state, pasid);

out_unregister:
- mmu_notifier_unregister(&pasid_state->mn, pasid_state->mm);
+ mmu_notifier_unregister(&pasid_state->mn, mm);

out_free:
- mmput(pasid_state->mm);
+ mmput(mm);
free_pasid_state(pasid_state);

out:
@@ -734,8 +750,18 @@ void amd_iommu_unbind_pasid(struct pci_dev *pdev, int pasid)
/* Clear the pasid state so that the pasid can be re-used */
clear_pasid_state(dev_state, pasid_state->pasid);

- /* This will call the mn_release function and unbind the PASID */
- mmu_notifier_unregister(&pasid_state->mn, pasid_state->mm);
+ /*
+ * Check if pasid_state->mm is still valid. If mn_release has already
+ * run it will be NULL and we can't (and don't need to) call
+ * mmu_notifier_unregister() on it anymore.
+ */
+ if (pasid_state->mm) {
+ /*
+ * This will call the mn_release function and unbind
+ * the PASID.
+ */
+ mmu_notifier_unregister(&pasid_state->mn, pasid_state->mm);
+ }

put_pasid_state_wait(pasid_state); /* Reference taken in
amd_iommu_pasid_bind */
--
1.7.9.5



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